Mounting system for a planetary gear train in a gas turbine engine

ABSTRACT

A mounting system for a planetary gear train in a gas turbine engine comprises a support strut, a deflection flange and a deflection limiter. The support strut extends between a stationary engine case and a rotating engine shaft that provides input to the planetary gear train in the gas turbine engine. The deflection flange extends from a rotating output component of the planetary gear train. The deflection limiter is connected to the support strut and engages the deflection flange when the gear train becomes radially displaced.

BACKGROUND

The present invention is directed to shaft arrangements in gas turbineengines. In particular, the present invention relates to an overhungmounting system for planetary gear trains.

In overhung mounting systems, a shaft within a gas turbine engine issupported by bearings at or near a first end, and a load is suspended,or cantilevered, at a second end of the shaft. Alternatives to overhungmounting systems include straddle mounting systems in which both ends ofthe shaft are supported by bearings and the load is positioned betweenthe bearings. In each configuration, a pair of spaced apart taperedroller bearings can be used to provide thrust reaction and shaftstiffening. Straddle mounting systems provide stability to the shaft,but typically require greater shaft lengths to support the set of rollerbearings in addition to a ball bearing. In gas turbine engines used aspropulsion systems for aircraft it is desirable to reduce engine lengthand weight, particularly in engines utilizing epicyclic gear trains thatuse additional axial space.

Fan drive gear systems use epicyclic gear trains to reduce the outputspeed of a gas turbine engine in order to drive a large diameter fan. Asthe bypass ratio of the engine increases, it becomes advantageous to usehigher gear reduction ratios. The epicyclic gear train is thenconfigured as a planetary gear system, rather than as a star gearsystem, to provide higher gear reduction ratios. Planetary gear systemsare supported axially between a gas turbine engine input shaft and anoutput fan shaft, and radially by a ground connection to a stationaryengine component. In such a configuration, as with all epicyclic geartrains, it is desirable to maintain proper alignment of the shafts inorder to reduce wear in the planetary gear system. Misalignment of theinput and output shafts can result in wear of gear teeth.

Various aircraft maneuvers impact alignment of gas turbine engineshafts, which induces vibration of gear trains. For example, highgravity turns or hard landing operations induce flexure of engine cases,sometimes referred to as backbone bending, that is transmitted to thegear train as a bending moment that shocks the gear teeth. It isadvantageous to permit the gear train to be radially displaced a limitedamount to absorb flexure without damaging the gear teeth. Thus, overhungmounting systems are typically used with epicyclic gear trains becauseof their ability to incorporate radial displacement with the use offlexible shafts. Overhung mounting systems, however, permit too muchflexure when support bearings are moved close to the gear train in anattempt to shorten engine length. There is, therefore, a need for anaxially short and radially flexible shaft mounting system suitable foruse with a planetary gear system.

SUMMARY

The present invention is directed to a mounting system for a planetarygear train in a gas turbine engine. The mounting system comprises asupport strut, a deflection flange and a deflection limiter. The supportstrut extends between a stationary engine case and a rotating engineshaft that provides input to the planetary gear train in the gas turbineengine. The deflection flange extends from a rotating output componentof the planetary gear train. The deflection limiter is connected to thesupport strut and engages the deflection flange when the gear trainbecomes radially displaced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-section of a gas turbine engine having afan drive gear system.

FIG. 2 shows a cross-section of a mounting system for a planetary geartrain used in the fan drive gear system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a schematic cross-section of gas turbine engine 10. Gasturbine engine 10 includes low pressure spool 12, high pressure spool 14and fan drive gear system 16. Low pressure spool includes low pressurecompressor 18 and low pressure turbine 20, which are connected by lowpressure shaft 22. High pressure spool 14 includes high pressurecompressor 24 and high pressure turbine 26, which are connected by highpressure shaft 28. Fan drive gear system 16 includes epicyclic geartrain 30 and fan assembly 32, which are connected by fan shaft 34.Epicyclic gear train 30 includes sun gear 36, ring gear 38 and planetarygear set 40. Low pressure spool 12 and high pressure spool 14 arecovered by engine nacelle 42, and fan assembly 32 and nacelle 42 arecovered by nacelle 44. Low pressure spool 12, high pressure spool 20 andfan assembly 32 comprise a two-and-a-half spool gas turbine engine inwhich epicyclic gear train 30 couples fan assembly 32 to low pressurespool 12 with input shaft 46.

Fan assembly 32 generates bypass air for producing thrust that isdirected between engine nacelle 42 and fan nacelle 44, and core air thatis directed into engine nacelle 42 for compressing sequentially with lowpressure compressor 18 and high pressure compressor 24. Compressed coreair is routed to combustor 48 wherein it is mixed with fuel to sustain acombustion process. High energy gases generated in combustor 48 are usedto turn high pressure turbine 26 and low pressure turbine 20. Highpressure turbine 26 and low pressure turbine 20 rotate high pressureshaft 28 and low pressure shaft 22 to drive high pressure compressor 24and low pressure compressor 18, respectively. Low pressure shaft 22 alsodrives input shaft 46, which connects to epicyclic gear train 30 todrive fan blades 50 of fan assembly 32.

Engine 10 is configured to operate at high bypass ratios, wherein theratio of bypass air to core air is large. Higher bypass ratios aregenerated by increasing the diameter of fan blades 50. Larger diameterfan blades are typically rotated at slower speeds than smaller blades toavoid performance issues related to blade tip speed, for example.Epicyclic gear train 30 is configured as a planetary gear system toprovide a high gear reduction ratio between input shaft 46 and fan shaft34. Planetary gear trains typically provide gear reduction ratios ofabout 3:1 or more. Epicyclic gear train 30 comprises a planetary gearsystem in which sun gear 36 and planetary gear set 40 rotate, while ringgear 38 remains stationary. Input shaft 46 provides rotational power tosun gear 36 of gear train 30. Planetary gear set 40, which is mounted toa carrier rack, rotates between sun gear 36 and ring gear 38 to drivefan shaft 34. Planetary gear set 40 and fan shaft 34 rotate about thecenterline of engine 10 at a slower rate than sun gear 36 and inputshaft 46. Fan shaft 34 drives fan assembly 32 to drive fan blades 50,which produce the bulk of the thrust generated by engine 10.

During operation of engine 10, various forces are applied to fan shaft34, gear train 30 and input shaft 46. For example, hard turningmaneuvers produced with fan blades 50 generate large gravitationalforces that impart bending moments in fan shaft 34. Flexure of shaft 34displaces gear train 30. Large displacements of gear train 30 causemisalignment between gear teeth of sun gear 36, ring gear 38 andplanetary gear set 40. Epicyclic gear train 30 is coupled to engine 10using a mounting system of the present invention to limit displacementof gear train 30, and to reduce the length of fan shaft 34. The mountingsystem includes deflection limiter 52 as well as other components thatare described in more detail with reference to FIG. 2.

FIG. 2 shows a cross-section of a mounting system for epicyclic geartrain 30 used in fan drive gear system 16 of FIG. 1. Gas turbine engine10, which is disposed about engine centerline CL, includes fan drivegear system 16, low pressure compressor 18, low pressure shaft 22,planetary gear train 30, output shaft 34, nacelle 42, input shaft 46,fan blade 50, deflection limiter 52, rotor 54, support strut 56, bearingassembly 58, flex coupling 60, support strut 62, bearing assembly 64 anddistribution system 66. Planetary gear train 30 includes sun gear 36,ring gear 38, planetary gear set 40, gear carrier 68, journal bearing70, planetary gear 72 and transfer bearing 74. Deflection limiter 52includes drum 76, head 78, bearing 80, damper 82 and hard stop 84.Distribution system 66 includes feed tube 86, plunger 88 and collar 90.

Planetary gear train 30 is supported within engine 10 by input shaft 46,output shaft 34, and the mounting system of the present invention, whichincludes deflection limiter 52 and flex coupling 60. Input shaft 46 andflex coupling 60 permit planetary gear train 30 to move within nacelle42 in order to absorb bending moments applied by output shaft 34.Deflection limiter 52 engages transfer bearing 74 to prevent gear train30 from being displaced past a threshold level. Transfer bearing 74 alsoengages distribution system 66 to provide lubricating oil to gear train30.

Low pressure shaft 22 extends from gas turbine engine 10 (FIG. 1) todrive input shaft 46. Low pressure compressor 18 is also coupled to lowpressure shaft 22 by rotor 54. Low pressure shaft 22 is supported withinnacelle 42 by strut 56, which connects to shaft 22 via bearing assembly58. In the embodiment shown, bearing assembly 58 includes a ballbearing. Input shaft 46 is connected to shaft 22 at a first end, and sungear 36 at a second end. Ring gear 38 is anchored to nacelle 42 (or anengine case for fan drive gear system 16 or low pressure compressor 18within nacelle 42) by flex coupling 60. Thus, ring gear 38 remainsstationary within nacelle 42 during operation of engine 10. Planetarygear set 40 is supported between sun gear 36 and ring gear 38 by gearcarrier 68. Gear carrier 68 comprises a pair of parallel platesconnected by journal bearing 70. Journal bearing 70 provides a pin uponwhich planet gear 72 rotates. Planetary gear set 40 includes a pluralityof journal bearings 70 and planet gears 72 (only one of each is shown inFIG. 2) which are distributed around centerline CL and connected to gearcarrier 68. At a first end, output shaft 34 is attached to a torqueframe (not shown) having fingers that connect to gear carrier 68. At asecond end, output shaft 34 connects to fan assembly 32 (FIG. 1) of fandrive gear system 16. Support strut 62 extends from nacelle 42 (or anengine case therein) to support output shaft 34 with bearing assembly64. In the embodiment shown, bearing assembly 64 includes a pair oftapered roller bearings.

During operation of engine 10, low pressure shaft 22 rotates to drivecompressor 18, which provides compressed air for combustion. The ballbearing of bearing assembly 58 accommodates rotation of shaft 22, aswell as axial displacement of shaft 22, such as from thermal growth.Support strut 56 rigidly supports bearing assembly 58 such that shaft 22is generally radially immobilized with respect to nacelle 42 near geartrain 30. Input shaft 46 is coupled to shaft 22, such as by a spline,and extends generally axially from shaft 22 to connect to sun gear 36,such as by a spline. Input shaft 46 is not directly supported bybearings so as to permit displacement of gear train 30. Rotation ofshaft 46 produces rotation of sun gear 36 about centerline CL. Sun gear36 causes planet gear 72 to rotate about journal bearing 70. Engagementof planet gear 72 with ring gear 38 causes planet gear 72 to revolvearound centerline CL, causing gear carrier 68 to rotate about centerlineCL also. Thus, shaft 46, sun gear 36 and gear carrier 68 rotate aboutcenterline CL, while journal bearing 70 and planet gear 72 orbitcenterline CL. Rotation of gear carrier 68 causes output shaft 34 torotate about centerline CL to drive fan blades 50. The pair of taperedroller bearing of bearing assembly 64 accommodates rotation of shaft 34,but provides resistance to axial loads, such as from thrust forces.Support strut 62 rigidly supports bearing assembly 64 such that shaft 34is generally radially immobilized with respect to nacelle 42 near geartrain 30.

Lubrication is provided to gear train 30 via distribution system 66.Feed tube 86 extends generally radially between collar 90 and transferbearing 74. Plunger 88 rides in collar 90 at a radially outer end, andrides against a land on transfer bearing 74 at a radially inner end.Feed tube 86 is supported within engine 10 by supports (not shown). Alubricant is provided to collar 90 from a source within engine 10. Thelubricant enters plunger 88 and travels through feed tube 86 to enter anaxially extending bore in the land of transfer bearing 74. From transferbearing 74 the lubricant travels into a manifold on gear carrier 68 toenter journal bearing 70, and for distribution to the gear teethinterfaces in planetary gear set 40 through various radial and axialpassages. The lubricant reduces wear on and ensures adequate cooling ofthe gear teeth.

Operation of engine 10 produces vibration of gear train 30 through shaft34. For example, changes in airflow across fan blade 50 generates momentstresses in shaft 34, which, if left unchecked, propagate to gear train30. Engine 10 includes a plurality of mounting means that controlvibration and displacement of gear train 30. Shafts 34 and 46 supportgear train 30 axially and provide a degree of radial support that isproportional to the flexibility of the shafts, as influenced by bearingassemblies 64 and 58, respectively. Gear train 30 is also supportedwithin engine 10 by flex coupling 60 and deflection limiter 52. Flexcoupling 60 provides radial support from strut 62 during all operationsof engine 10. Deflection limiter 52 engages transfer bearing 74 toprovide a second radial support means during operations of engine 10that induce high bending moments of shaft 34.

Bearing assembly 64 provides gear train 30 with a first degree ofstability. Deflection of output shaft 34 is dampened by bearings 92A and92B to reduce the amount of vibration passed on to gear train 30.Bearings 92A and 92B stiffen shaft 34 to inhibit flexure induced bybending moments from blade 50. Bearing assembly 64 is positioned closeto gear train 30 to reduce the axial space occupied by fan drive gearsystem 16 and the length of engine 10. Furthermore, bearing 92A and 92Bare close coupled such that they are positioned closer to each otherthan in previous designs. In one embodiment, bearings 92A and 92B arespaced apart from about 1 inch (˜2.54 cm) to about 2 inches (˜5.08 cm).As such, the length of fan drive gear system 16 and gear train 30 isreduced. The arrangement of bearing assembly 64 in engine 10, however,limits the ability of bearings 92A and 92B to stiffen shaft 34.

Flexible shaft 46 absorbs movement of gear train 30 imparted by shaft34. Flexible shaft 46 allows gear train 30 to displace as shaft 34flexes. Specifically, input shaft 46 comprises a flexible shaft thatincludes undulations or bends that permit flexure of the shaft. Suchshafts are described in greater detail in U.S. Pat. No. 5,433,674 toSheridan et al., which is assigned to United Technologies Corporation,Hartford, Conn. As such, shaft 46 permits gear train to move with shaft34 to maintain proper alignment of gear teeth.

To further dampen displacement, gear train 30 is provided with directcoupling means to a stationary component within engine 10. Ring gear 38is connected to strut 62 by flex coupling 60. Flex coupling 60 comprisesa spring-like member that absorbs movement of gear train 30 and providesresistance to radial movement of gear train 30. Similar flex couplingsare described in U.S. Pat. No. 6,223,616 to Sheridan, which is assignedto United Technologies Corporation, Hartford, Conn., and theaforementioned U.S. Pat. No. 5,433,674. During most operations of engine10, bearing assembly 64, flex coupling 60 and flexible shaft 46 providethe requisite level of vibration damping and stability to gear train 30to avoid mashing of gear teeth within gear train 30. However, severedisplacement of gear train 30 from shaft 34 is undesirable, as can occurunder extreme operating conditions.

Engine 10 is provided with deflection limiter 52 to dampen and limitdisplacement of gear train 30 under extreme conditions. Specifically,transfer bearing 74 of gear carrier 68 is configured to engage drum 76of deflection limiter 52. Drum 76 comprises an axially extending annularbarrel having first rim 94 and second rim 96, between which extend aplurality of deflectable spokes 98. As such, drum 76 resembles a cageand is sometimes referred to as a “squirrel cage.” Such drums or cagesare described in U.S. Pat. No. 4,084,861 to Greenberg et al., which isassigned to United Technologies Corporation, Hartford, Conn. Second rim96 is connected to strut 56, and first rim 94 is cantilevered radiallyoutward of transfer bearing 74. Transfer bearing 74 comprises an axiallyextending flange that rotates with planetary gear set 40 about enginecenterline CL. Transfer bearing 74 provides a platform for engagingbearing 80 of deflection limiter 52 and receiving lubricating oil fromdistribution system 66. Bearing 80 is spaced from transfer bearing 74during normal operation of engine 10 such that shaft 34 supports geartrain 30 in an overhung configuration.

When shaft 34 is subject to a bending moment that causes gear train 30to be displaced past a threshold level, bearing 80 engages transferbearing 74. The threshold level corresponds to the magnitude of thebending moment in shaft 34 needed to displace gear train 30 the distancebetween bearing 80 and transfer bearing 74, which is typically set belowthe maximum bending moment shaft 34 is able to withstand. Damper 82 ofdeflection limiter 52 prevents drum 76 from deflecting too rapidly toavoid impact loading of the gear teeth in gear train 30. Damper 82 ispositioned between head 78 and hard stop 84. In one embodiment, damper82 comprises a squeeze film damper, as is described in theaforementioned U.S. Pat. No. 4,084,861. In such an embodiment, oil, suchas from feed tube 86, is contained between head 78 and hard stop 84 by apair of o-rings. As shaft 34 displaces gear train 30, spokes 98 of drum76 deflect as transfer bearing 74 pushes bearing 80. In the embodimentshown, bearing 80 comprises a roller bearing. Damper 82 is engaged atall times while transfer bearing 74 is engaged with bearing 80.Engagement of bearing 80 with transfer bearing 74 allows output shaft 34to resist bending movements imparted by blades 50. The amount ofresistance provided by drum 76 and damper 82 can be set to vary based ondifferent engine configurations. For example, the stiffness of drum 76can be varied by changing the cross-section profile of spokes 98, andthe amount of resistance provided by damper 82 can be varied by changingthe oil pressure between the o-rings. Shaft 34 supports gear train 30 ina straddle configuration when gear train 30 is displaced beyond thethreshold level and bearing 80 engages transfer bearing 74. Thus, themounting system of the present invention shifts from an overhungmounting configuration to a straddle mounting configuration. Hard stop84 prevents output shaft 34 from flexing beyond its maximum stresslevel. Hard stop 84 is disposed radially outward of head 78 and extendfrom strut 56.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A mounting system for a planetary geartrain in a gas turbine engine, the mounting system comprising: a supportstrut extending between a stationary engine case and a rotating engineshaft that provides input to the planetary gear train; a deflectionflange extending from a rotating output component of the planetary geartrain; and a deflection limiter comprising: a drum connected to thesupport strut, the drum engaging the deflection flange of the planetarygear train when the gear train becomes radially displaced; and a hardstop extending from the support strut and configured to prevent the drumfrom engaging the support strut when the gear train becomes radiallydisplaced.
 2. The mounting system of claim 1 wherein the planetary geartrain comprises: a sun gear for receiving input from the engine shaft; aring gear concentrically disposed about the sun gear; a planetary gearset disposed between the sun gear and the ring gear; and a gear carriercomprising the rotating output component coupled to the planetary gearset for connecting to an output shaft.
 3. The mounting system of claim 1wherein the deflection limiter comprises: a flexible drum comprising: afirst end connected to the support strut; and a second endconcentrically disposed about the deflection flange; and a bearingpositioned between the second end and the deflection flange.
 4. Themounting system of claim 3 wherein the: hard stop engages a radiallyoutward surface of the second end of the flexible drum when the geartrain becomes radially displaced.
 5. The mounting system of claim 4 andfurther comprising: a damper positioned between the flexible drum andthe support strut.
 6. The mounting system of claim 5 wherein the dampercomprises a squeeze film damper positioned between the second end of theflexible drum and the hard stop.
 7. The mounting system of claim 3wherein the flexible drum is a squirrel cage having: a first annular rimincluding the first end; a second annular rim including the second end;and a plurality of deflectable spokes extending between the firstannular rim and the second annular rim.
 8. The mounting system of claim3 and further comprising: a second support strut for extending from theengine case; and a pair of close coupled tapered bearings mounted to thesecond support strut for engaging the output shaft.
 9. The mountingsystem of claim 8 and further comprising: a flex coupling for groundingthe ring gear to the engine case.
 10. An aircraft propulsion systemcomprising: a gas turbine engine; an input shaft driven by the gasturbine engine; a planetary gear train comprising: a sun gear connectedto the input shaft; a ring gear concentrically disposed about the sungear; a planetary gear set disposed between the sun gear and the ringgear; and a rotatable gear carrier coupled to the planetary gear set; anoutput shaft connecting to the gear carrier to a fan propeller; anengine case surrounding the input shaft, gear train and output shaft;and a flexible cantilevered deflection limiter comprising: a first endconnected to the engine case; and a second end axially extending fromthe first end; and an axially extending deflection flange connected tothe planetary gear train and extending to be concentric with the secondend of the flexible cantilevered deflection limiter; wherein theflexible cantilevered deflection limiter is spaced from the axiallyextending deflection flange and is configured to engage the axiallyextending deflection flange when the output shaft deflects past athreshold level.
 11. The propulsion system of claim 10 wherein theflexible cantilevered deflection limiter comprises: a flexible drum; anda bearing positioned between the second end and the deflection flange.12. The propulsion system of claim 11 and further comprising: a firstsupport strut extending from the engine case to engage the input shaftat a first bearing interface; and a second support strut extending fromthe engine case to engage the output shaft at a second bearinginterface, the second bearing interface comprising a pair of closecoupled tapered bearings.
 13. The propulsion system of claim 11 andfurther comprising: a damper positioned between the flexible drum andthe support strut.
 14. The propulsion system of claim 13 wherein thedamper comprises a squeeze film damper positioned between the second endof the flexible drum and the hard stop.
 15. The propulsion system ofclaim 11 wherein the flexible drum is a squirrel cage having: a firstannular rim including the first end; a second annular rim including thesecond end; and a plurality of deflectable spokes extending between thefirst annular rim and the second annular rim.
 16. The propulsion systemof claim 12 and further comprising: a flex coupling connecting theengine case to the ring gear.
 17. A planetary gear train for use in agas turbine engine, the planetary gear train comprising: a sun gearrotatable by a shaft of the gas turbine engine; a ring gearconcentrically disposed about the sun gear for grounding to a stationaryengine component; a planetary gear carrier having a plurality ofplanetary gears disposed between the sun gear and the ring gear suchthat the carrier is rotatable about the sun gear; and a deflectionlimiter comprising: a support flange extending axially from the gearcarrier; a flexible drum for anchoring by the stationary enginecomponent and extending to be concentrically aligned with the supportflange.
 18. The planetary gear train of claim 17 and further comprising:a bearing positioned between the support flange and the flexible drum.19. The planetary gear train of claim 18 and further comprising a hardstop positioned between the stationary engine component and the flexibledrum.
 20. The planetary gear train of claim 19 and further comprising asqueeze film damper positioned between the hard stop and the flexibledrum.
 21. A mounting system for a planetary gear train in a gas turbineengine, the mounting system comprising: a support strut extendingbetween a stationary engine case and a rotating engine shaft thatprovides input to the planetary gear train; a deflection flangeextending from a rotating output component of the planetary gear train;a deflection limiter connected to the support strut, the deflectionlimiter engaging the deflection flange of the planetary gear train whenthe gear train becomes radially displaced; a feed tube configured toprovide lubrication to the planetary gear train; and a damper positionedbetween the deflection limiter and the support strut, the damperconfigured to receive lubricant from the feed tube.
 22. A mountingsystem for a planetary gear train in a gas turbine engine, the mountingsystem comprising: a support strut extending between a stationary enginecase and a rotating engine shaft that provides input to the planetarygear train; a deflection flange extending from a rotating outputcomponent of the planetary gear train; a deflection limiter connected tothe support strut, the deflection limiter engaging the deflection flangeof the planetary gear train when the gear train becomes radiallydisplaced; and a bearing mounted to the deflection flange and spacedfrom the deflection limiter such that the deflection limiter engages thebearing when the gear train becomes radially displaced.
 23. A mountingsystem for a planetary gear train in a gas turbine engine, the mountingsystem comprising: a support strut extending between a stationary enginecase and a rotating engine shaft that provides input to the planetarygear train; a deflection flange extending from a rotating outputcomponent of the planetary gear train; and a deflection limiterconnected to the support strut, the deflection limiter engaging thedeflection flange of the planetary gear train when the gear trainbecomes radially displaced; wherein the deflection flange comprises atransfer bearing for a lubrication system coupled to the planetary geartrain.
 24. A mounting system for a planetary gear train in a gas turbineengine, the mounting system comprising: a support strut extendingbetween a stationary engine case and a rotating engine shaft thatprovides input to the planetary gear train; a deflection flangeextending from a rotating output component of the planetary gear train;and a deflection limiter connected to the support strut, the deflectionlimiter engaging the deflection flange of the planetary gear train whenthe gear train becomes radially displaced; wherein the deflectionlimiter comprises a flexible drum comprising: a first end connected tothe support strut, the first end comprising a first annular rim; asecond end concentrically disposed about the deflection flange, thesecond end comprising a second annular rim; and a plurality ofdeflectable spokes extending between the first annular rim and thesecond annular rim.